Novel medical therapies, diagnostics and cures previously not imagined are emerging from the refined map of the human genome. The application of genomics and proteomics has provided new means for recognizing the molecular basis of numerous diseases and identifying novel drug targets for pharmacological intervention and diagnostics. We are undergoing a renaissance in personalized medical care and tailored therapy. Novel prognostic and diagnostic targets based on serum, biopsy and image based assessment promise to increase patient-specific information. Routinely used methodologies to study biological processes are based on destructive sampling of biological material, thus allowing the researcher to witness only a static snapshot taken at the respective experimental endpoint. The evolution of live-cell fluorescence microscopy, fluorescence and bioluminescence imaging as well as non-invasive imaging of targeted injectable tracers have revolutionized our understanding of many processes at the molecular and cellular levels, With the development of suitable probes and instrumentation for functional imaging In vivo, our ability to identify and measure biological processes in real-time has progressively extended to the whole organism, from mice to humans. This new set of molecular probes, detection technologies and imaging strategies, collectively termed "molecular imaging" (1-9), is providing biologists and clinicians with exciting new opportunities to perform noninvasive and longitudinal studies of dynamic biological processes in intact cells and live animals. In the last five years, a series of ground-breaking studies have demonstrated that molecular imaging is a powerful tool that enables visualization of gene expression, biochemical reactions, signal transduction and regulatory pathways in whole organisms in vivo.